Add missing letter.odt in package

issue3864
(grafted from f506ee0dda9b8a3c7a439f5165285cf8d23ab28a)

--HG--
branch : 3.0
extra : source : f506ee0dda9b8a3c7a439f5165285cf8d23ab28a
Prepare release 3.0.3

--HG--
branch : 3.0
Added tag 3.0.3 for changeset e8f73a579f07

--HG--
branch : 3.0
Increase version number

--HG--
branch : 3.0